Regulated pre-messenger RNA processing is nearly ubiquitous among eukaryotes but has been studied mainly in metazoans, where the complexity of the biological processes it controls have posed many challenges. The overall goal of the proposed research is to use a combination of genetic, genomic and molecular tools uniquely available in the fission yeast Schizosaccharomyces pombe to fill this gap in our understanding. In recent work, thirteen meiotically spliced transcripts were discovered and two pre-mRNAs that encode cyclins investigated in detail. These studies revealed that splicing of rem1 and crs1 is restricted to meiosis by a novel inhibitory mechanism that requires non-intronic elements located outside the coding regions, a considerable distance from the target introns. While this shared (and highly unusual) regulatory strategy suggests similarities between crs1 and rem1, their splicing is temporally and mechanistically distinct: the identity of the major element that prevents crs1 splicing in vegetative cells and the nature of a recently discovered trans-acting factor suggest a role for the polyadenylation machinery, while the location of the major rem1 element together with the effects of heterologous expression on splicing suggest a role for the transcription machinery. Three specific aims will be pursued. To test the hypothesis that genetic circuits regulated at the level of splicing contribute to meiotic differentiation, additional new meiotically spliced transcripts will be identified and characterized with respect to kinetics of splicing, shared regulatory mechanisms, and hierarchical organization. To gain further mechanistic insight into the regulation of rem1 and crs1 splicing, the cis-acting elements responsible for both suppression of splicing in vegetative cells and positive control in meiotic cells will be pinpointed via analysis of chimeric constructs and mutagenesis. This information will be used in the design of both open-ended and candidate gene strategies to identify trans- acting factors, among which may be novel players that mediate communication between the machineries that carry out different steps in gene expression. Thus, this research provides an unprecedented opportunity to explore the function of the mRNA production factory in a native biological context. The insights gained will ultimately relate to human health and developmental disabilities, as aberrant gene expression is an underlying cause of numerous diseases.